Reduction of sulfoxides and pyridine-N-oxides over iron powder with water as hydrogen source promoted by carbon dioxide

Abstract

A green process was developed for efficient reduction of sulfoxides and pyridine-N-oxides using the iron powder in the presence of H₂O–CO₂ to sulfides and pyridines, respectively. Notably, H₂O is employed as the terminal hydrogen source, and CO₂ could enhance hydrogen generation through in situ formation of carbonic acid. Thus carbonic acid offers simple neutralization by depressurizing CO₂ and the system can eliminate unwanted byproducts. The high generality and chemo-selectivity of this protocol were demonstrated by the scope of substrates, in which chlorine, vinyl group and benzene ring can be tolerated.